A system for manufacturing high-quality semiconductor single crystals, and a method for manufacturing high-quality semiconductor single crystals.

Abstract

To provide a system and method for growing a bulk semiconductor single crystal, more concretely, growing a bulk semiconductor single crystal, such as silicon carbide on the basis of physical vapor phase transportation.SOLUTION: A sublimation system for growing at least one single crystal of a semiconductor material by a sublimation growth method includes: a crucible (102) having a longitudinal axis (120) and including fixing means for fixing at least one seed crystal (110) and at least one raw material division (104) for storing a raw material (108); a heating system formed so as to form an irregular temperature field around the circumference of the crucible (102) and / or along the longitudinal axis of the crucible (102); and a heat insulation unit (117) at least partially surrounding the crucible (102). The heat insulation unit (117) has a form asymmetric in the diameter direction and / or the axial direction for compensating the irregular temperature field .SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a system and method for growing a bulk semiconductor single crystal, and more specifically, for growing a bulk semiconductor single crystal such as silicon carbide based on physical vapor transport.

Background Art

[0002] Silicon carbide (SiC) substrates are widely used in the manufacture of electronic devices. Using appropriate raw materials, SiC single crystals are generally grown by physical vapor growth (PVT) methods as shown, for example, in U.S. Patent Application Publication No. 8865324 (B2). Then, an SiC substrate is manufactured from the bulk single crystal using filament cutting (sawing) or another suitable separation method, and its surface is then refined in a multi-step polishing process. In a subsequent epitaxial process, thin single crystal layers (e.g., SiC, GaN) are deposited on the SiC substrate. The properties of these layers and the electronic components manufactured therefrom are critically determined by the quality of the SiC substrate.

[0003] For crystal growth by PVT, a crystal growth system that is resistively heated or inductively heated is usually used. The so-called reactor serves as the nucleus of the sublimation system, where actual crystal growth takes place. A growth structure consisting of an insulator, a crucible made of graphite and carbon materials or heat-resistant metal or a combination thereof, a seed material, and a raw material is placed inside the reactor. Heating is provided either by an induction coil placed outside the reactor or by a resistance heater placed inside the reactor. Inside the crucible, the SiC raw material is sublimated and deposited (i.e., reverse sublimated) on the SiC seed crystal. In this way, an SiC single crystal boule is grown. FIG. 11 shows such a conventional inductively heated PVT system 800.

[0004] The growth mechanism 800 comprises a growth crucible 802 including a SiC supply region 804 and a crystal growth region 806. Powdered SiC raw material 808 is injected into the SiC supply region 804 of the growth crucible 802 as a pre-processed starting material before the start of the growth process, and is placed, for example, in the SiC supply region 804. The raw material 808 may be densified or provided as a partially or completely solid material to increase the density of the raw material. A seed crystal 810 is provided in the crystal growth region 806, on the inner wall of the growth crucible 802 facing the SiC supply region 804, for example, on the lid 812 of the crucible. The bulk SiC single crystal to be grown grows on the seed crystal 810 by deposition from the SiC growth gas phase formed in the crystal growth region 806. The bulk SiC single crystal to be grown and the seed crystal 810 may have approximately the same diameter.

[0005] The growing crucible 802, including the crucible lid 812, may be manufactured from a conductive and thermally conductive graphite crucible material. A thermal insulator (not shown in the figure) is placed around it, which may include, for example, a porosity of a crystalline graphite insulating material, particularly higher than that of the graphite crucible material.

[0006] A heat-insulated growth crucible 802 is placed inside a tubular container 814, which may be constructed as a quartz glass tube and form an autoclave or reactor. An induction heating device in the form of a heating coil 816 is placed around the container 814 to heat the growth crucible 802. The growth crucible 802 is heated by the heating coil 816 to a growth temperature exceeding 2000°C, particularly up to about 2200°C. The heating coil 816 inductively couples an electric current into the conductive crucible wall (so-called susceptor) of the growth crucible 802. This current flows substantially as a circulating current in the circular, hollow, cylindrical crucible wall, heating the growth crucible 802 in the process. The susceptor may be made from graphite, TaC, WC, Ta, W, or other heat-resistant metals. The primary purpose of the susceptor is to provide a heat source inside the crucible 802. When the susceptor is heated by induction, its surface reaches a high temperature, and that temperature is then transferred to the inside of the crucible 802 through conduction and / or radiation.

[0007] As described above, the induction coil 816 is mounted on the outside of the glass tube 814 and is usually surrounded by a Faraday cage (not visible in the drawing) that forms an electromagnetic shield to block electromagnetic radiation. The induction coil 816 has equidistant windings, with each winding at a distance d_1 from the adjacent winding.

[0008] Furthermore, in conventional resistance heating PVT systems, the heating resistance element is mounted inside the reactor. If the reactor is made of metal, it can be cooled by water or air. Examples of heating resistance PVT systems are described in the published patent applications U.S. Patent Application Publication No. 2016 / 0138185(A1) and U.S. Patent Application Publication No. 2017 / 0321345(A1).

[0009] The temperature is measured by one or more pyrometers or one or more thermocouples. The vacuum-sealed reactor can be evacuated by one or more vacuum pumps. Furthermore, the system can receive an inert gas or doped gas through one or more gas supply lines, and the pressure within the system can be measured and controlled. All process parameters (pressure, temperature, gas flow rate, etc.) can be set, controlled, and stored by a computerized system control unit. The sublimation system control unit communicates with all relevant components (e.g., transducers, pyrometers, vacuum control valves, mass flow controllers (MFCs), pressure gauges).

[0010] Growing SiC single crystals using the PVT method requires a homogeneous temperature profile as close to the specified temperature as possible. The deposition of silicon and carbon atoms, as well as compounds, onto the seed follows this temperature field. Typically, the temperature field within the growth zone is selected to form a convex crystal that is longer in the center than in the edge region. This is to avoid the inward growth of edge defects that can occur as the growing crystal comes into contact with the surrounding reactor.

[0011] For the growth of high-quality crystals, homogeneous heat distribution within the growth crucible is crucial. By distributing heat as homogeneously as possible, the crystals should grow as homogeneously and symmetrically as possible. This requires avoiding different growth rates around the crystal's periphery.

[0012] Different growth rates along the circumference of the crystal lead to an increased appearance of edge defects. Therefore, in areas with low growth rates (caused by locally high temperatures), increased material wear can occur in adjacent reactor material, causing the material to melt and fall into areas intended for usable crystal diameter, thus reducing the usable crystal diameter. Observable defect patterns include carbon inclusions and / or carbon particles. Similarly, local temperature differences within the edge region can interrupt or disrupt the step flow necessary for the growth of polytype 4H-SiC, leading to polytype changes, and subsequently, undesirable heterogeneous polytypes (e.g., 6H, 15R) can spread from the edge region towards the center of the crystal. This also reduces the usable crystal diameter.

[0013] Different growth rates in the periphery of the crystal also cause disorder in the crystal lattice and stress within the crystal, which leads to dislocation formation.

[0014] All of these defects lead to a decrease in the quality of the grown single-crystal boules, and therefore to a decrease in the yield of single-crystal SiC substrates produced from them, which may be suitable for electronic equipment manufacturing.

[0015] To date, the impact of the growth system has been underestimated, and this is becoming increasingly clear, especially with respect to continuously increasing crystal diameter. Conventional growth systems have primarily attempted to improve crystal quality by optimizing the insulating structure itself.

[0016] For example, European Patent Application Publication No. 3699328(A1) describes a method for improving the quality of SiC single crystals, particularly by using homogeneous insulation. A multi-component design of insulating cylindrical bodies and their corresponding alignments are intended to compensate for the inherent material heterogeneity. However, the use of optimized insulation is not always sufficient to compensate for unfavorable design of the growth system, especially in the case of continuously increasing crystal diameters.

[0017] Furthermore, German Patent No. 102009004751(B4) discloses a method for homogenizing insulation by reducing localized hot spots using short carbon fibers. The use of these short carbon fibers reduces the coupling of induced magnetic fields into the insulating material, thereby reducing the generation of ring currents and localized hot spots in the insulating material. However, the use of such optimized insulation is not sufficient to compensate for the unfavorable design of the growth system, especially in the case of continuously increasing crystal diameters.

[0018] Even the highest requirements for growth equipment design—generating a homogeneous, ideally radially symmetric temperature field—still frequently result in crystals with edge defects, as described above. This is believed by the inventors to be because, despite manufacturing all necessary structural elements from materials such as plastic, rigid paper, or similar composite and structural materials, the structural elements still influence the temperature conduction from the induced magnetic field and / or resistive heater. [Prior art documents] [Patent Documents]

[0019] [Patent Document 1] U.S. Patent Application Publication No. 8865324(B2) [Patent Document 2] U.S. Patent Application Publication No. 2016 / 0138185(A1) [Patent Document 3] U.S. Patent Application Publication No. 2017 / 0321345 (A1) Specification [Patent Document 4] European Patent Application Publication No. 3699328 (A1) Specification [Patent Document 5] German Patent No. 102009004751 (B4) Specification [Patent Document 6] European Patent Application Publication No. 2664695 (B1) Specification [Summary of the Invention]

[0020] The present invention has been made in view of the drawbacks and inconveniences of the prior art, and its object is to provide a system for growing a single crystal of a semiconductor material by physical vapor transport (PVT), and a method for manufacturing a single crystal of a semiconductor material with improved single crystal quality and high cost-effectiveness.

[0021] This object is solved by the subject matter of the independent claims. Advantageous embodiments of the present invention are the subject matter of the dependent claims.

[0022] Based on the idea that the present invention can grow a high-quality crystal with as few edge defects as possible even when using a growth system that generates a non-uniform temperature field by using a special isolation design.

[0023] Specifically, a sublimation system for growing at least one single crystal of a semiconductor material by a sublimation growth method includes a crucible. The crucible has a longitudinal axis and includes fixing means for at least one seed crystal, and further includes at least one raw material section for containing a raw material. The sublimation system further includes a heating system formed to generate an irregular temperature field around the circumference of the crucible and / or along the longitudinal axis of the crucible. A thermal insulation unit surrounds the crucible at least partially and has a radially and / or axially asymmetric configuration for compensating the irregular temperature field. The introduction of this targeted asymmetric insulation into the asymmetric growth system, combined with each other, results in a homogeneous temperature field in the growth chamber. As a result, a homogeneous and edge-defect-free SiC single crystal can be grown.

[0024] For example, inhomogeneities in the density, porosity, thermal conductivity, and / or electrical conductivity of an insulating material can lead to local differences in the quality of heat insulation and dissipation. Therefore, these inhomogeneities affect the temperature distribution within the growth crucible. According to the present invention, the intentional insertion of such inhomogeneities through the manipulation of the insulation structure is achieved through the introduction of steps, cuts, or through densification by local shaving, edging, groove formation, or clamping or stitching, etc. Therefore, the inhomogeneities of the insulating material may be used to cancel out the inhomogeneities caused by the asymmetry within the heating system.

[0025] Specifically, the thickened portion or overlap of the thermal insulation unit can reduce heat loss and thus cancel out the "cold spots" within the temperature field generated by the heating system. On the other hand, the gaps or thinned regions of the thermal insulation unit can increase heat loss and thereby offset the "hot spots" within the temperature field generated by the heating system. Information regarding the actual asymmetry within the heating system can be obtained using spatial decomposition 3D measurements of the temperature field and / or electromagnetic field generated by the heating system during operation.

[0026] For example, a heating system may include an induction coil and / or a resistance heating coil, both capable of generating an electromagnetic field, with the coils at least partially surrounding the crucible. In the case of induction heating, the coils are located outside the reactor, while in the case of resistance heating, the coils are located inside the reactor. Advantages of induction heating include strict control over critical temperatures within the growth chamber, a non-contact method of heating the crucible, and the ability to be implemented in a changing atmosphere. General advantages of resistance heating systems over other types of heating systems are their high electrical efficiency and less complex control.

[0027] According to a favorable example of this disclosure, a thermal insulation unit comprises needle-processed carbon felt and / or densified carbon short fibers. Carbon felt is a flexible insulating material for high-temperature applications in an inert or vacuum atmosphere and consists of carbon fibers stabilized by needle processing. For example, a base material for producing carbon and graphite soft felt is felt made from needle-processed cellulose fibers. These are processed into carbon soft felt by thermal processing at 800–1000°C. When these felts are treated at even higher temperatures above 2000°C, the carbon fibers gradually acquire a graphite-like structure, becoming so-called "graphite soft felt," but without actually being given a graphite structure.

[0028] In the sense of this disclosure, carbon short fibers are intended to mean insulating materials comprising carbon fibers having a fiber length in the range of 1 mm to 10 mm and a fiber diameter in the range of 0.1 mm to 1 mm, as disclosed, for example, in German Patent No. 102009004751(B4).

[0029] To facilitate the manufacture and assembly of the thermal insulation unit, the thermal insulation unit comprises a flexible sheet of carbon material, which is rolled around a crucible and includes seams, at least one fastener, and / or overlapping areas.

[0030] By utilizing the asymmetry of thermal insulation, it is possible to compensate for technically unavoidable asymmetries within growth systems, particularly within heating systems.

[0031] Asymmetry in the temperature field generated by a heating system can occur in various forms. In the case of induction heating, the heating system may include, for example, metal support members. In such cases, there are particularly clearly defined locations of asymmetry, and thus asymmetric arrangements for cancellation within a thermal insulation unit can be achieved particularly easily.

[0032] An alternative to non-uniform heating may occur when using a heating system in which the coil has a deformed cross-section in at least one of its windings, and / or the coil has at least one winding that is positioned at different distances from adjacent windings.

[0033] Furthermore, the coil may have at least one electrical contact positioned in an axial location close to the crucible.

[0034] A particularly stable geometric shape can be achieved when the thermal insulation unit has a cylindrical shape in which the wall thickness changes around the circumference.

[0035] Another possibility for introducing the desired asymmetry into a thermal insulation unit can be realized if the thermal insulation unit comprises one or more micro-holes that form at least one gap or groove.

[0036] Furthermore, the thermal insulation unit may be formed from a plurality of separate parts assembled to have radial and / or axially extending connections.

[0037] When planar sheets are used as the starting material for a thermal insulation unit, the sheets of insulating material are arranged around a crucible to form abutment joints, inclined abutment joints, and / or overlapping joints.

[0038] This disclosure further relates to a method for growing at least one single crystal of a semiconductor material by sublimation growth, wherein this method is A crucible having a longitudinal axis is prepared, at least one seed crystal is fixed to the fixing means of the crucible, and raw materials are filled into at least one raw material compartment. This includes using a heating system to generate an irregular temperature field around the circumference of the crucible and / or along the longitudinal axis of the crucible, A thermal insulation unit is provided that at least partially surrounds the crucible, and the thermal insulation unit has a radially and / or axially asymmetrical configuration for compensating for irregular temperature fields.

[0039] Advantageously, the temperature field acting on the growing single crystal causes the growth rate, measured around a defined circumference of the single crystal, to differ by at least 0.1 μm / h to 10 μm / h, preferably 0.7 μm / h, at any two points along the circumference. The growth rate is measured after the growth process is complete by determining the final geometric shape using a dial gauge or the like, along with knowledge of the applied growth time.

[0040] Advantageously, the temperature field acting on the growing single crystal gives the final grown single crystal a distribution of length values ​​between the back surface and the top surface of the single crystal, measured along a defined circumference of the single crystal, where the length values ​​differ from the average value by 10% or less, preferably 5% or less.

[0041] When measuring the height of the final grown single crystal, the defined circumference is either the outer circumference of the final grown single crystal, or the radial distance from the center of the final grown single crystal, corresponding to the diameter of the wafer produced from the final grown single crystal.

[0042] The accompanying drawings are incorporated herein by reference and form part of this specification to illustrate several embodiments of the present invention. These drawings, together with the description, serve to illustrate the principles of the present invention. The drawings are intended solely to illustrate preferred and alternative examples of how the present invention may be made and used, and should not be construed as limiting the present invention to the embodiments illustrated and described. Furthermore, several aspects of the embodiments may, individually or in different combinations, form solutions according to the present invention. Thus, the following detailed embodiments may be considered individually or in any combination thereof. Further features and advantages will become apparent from a more detailed description of the various embodiments of the present invention illustrated in the accompanying drawings. In the accompanying drawings, similar reference numerals refer to similar elements. [Brief explanation of the drawing]

[0043] [Figure 1] This is a schematic cross-sectional side view of a sublimation system according to the first example. [Figure 2] This is a schematic side view of a thermal insulation unit according to the first example. [Figure 3] A schematic side view of a thermal insulation unit with further examples. [Figure 4] A schematic side view of a thermal insulation unit with further examples. [Figure 5] A schematic top view of a thermal insulation unit with further examples. [Figure 6] A schematic side view of a thermal insulation unit with further examples. [Figure 7] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 8] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 9] A schematic top view of a sublimation system with further examples. [Figure 10] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 11] This is a schematic cross-sectional side view of a known sublimation system. [Modes for carrying out the invention]

[0044] The present invention will now be described in detail with reference to the figures, starting with Figure 1.

[0045] Figure 1 shows a sublimation system 100 according to a first example of the present disclosure. Note that the term sublimation system is intended to encompass any system for growing at least one single crystal of a semiconductor material using sublimation growth. Preferably, the term refers to a physical vapor transport (PVT) system for growing a silicon carbide (SiC) volume single crystal, as described with reference to Figure 11.

[0046] The sublimation system 100 includes a growth crucible 102, which includes raw material compartments, in particular a SiC supply area 104 and a crystal growth area 106. The SiC raw material 108 may be in powder form and, before the start of the growth process, is injected into the SiC supply area 104 of the growth crucible 102 as a pre-processed starting material, and is placed, for example, in the SiC supply area 104. The raw material 108 may be densified to increase the density of the raw material 108, or may be provided as a partially or completely solid material.

[0047] The seed crystal 110 is provided in the crystal growth region 106, on the inner wall of the growth crucible 102 facing the SiC supply region 104, for example, on the lid 112 of the crucible. The bulk SiC single crystal to be grown grows on the seed crystal 110 by deposition from the SiC growth gas phase formed in the crystal growth region 106. The growing bulk SiC single crystal and the seed crystal 110 may have approximately the same diameter. If the diameter of the crystal channels is larger than the diameter of the seed crystal, the growing bulk SiC single crystal may have a larger diameter than the seed crystal 110. However, the usable low-defect diameter of the growing bulk SiC single crystal is usually the same size as the diameter of the seed crystal.

[0048] The growing crucible 102, including the crucible lid 112, may be manufactured from a conductive and heat-conductive graphite crucible material. A thermal insulation unit 117 is placed around it, which may include, for example, a porosity of a crystalline or felt-like graphite insulating material, particularly one with a higher porosity than the graphite crucible material. Transparent windows 119 are provided on one or both of the axial end regions of the thermal insulation unit 117. These transparent windows 119 can be used to measure the temperature of the crucible 102.

[0049] In induction heating, the thermally insulated growth crucible 102 is placed inside a tubular container (not shown in Figure 1), which may be a quartz glass tube forming an autoclave or reactor. An induction heating device in the form of a heating coil 116 is positioned around the container to heat the growth crucible 102. The heating coil 116 generates the required temperature field by inductively coupling an electric current within the conductive crucible wall (susceptor) of the growth crucible 102. This current flows substantially as a circulating current circumferentially within the circular, hollow, cylindrical crucible wall, heating the growth crucible 102 in the process. The susceptor can be made from graphite, TaC, WC, Ta, W, or other heat-resistant metals, and may be an integral part of the crucible 102 or a separate part close to the crucible wall. The primary purpose of the susceptor is to provide a heat source inside the crucible 102. When the susceptor is heated by induction, its surface reaches a high temperature, and that temperature is then transferred to the inside of the crucible 102 through conduction and / or radiation.

[0050] As described above, in the case of induction heating, the coil 116 is mounted on the outside of the glass tube and is usually surrounded by a Faraday cage (not visible in Figure 1) to block electromagnetic radiation. In the case of resistance heating, the coil 116 is also mounted inside the reactor and in thermal insulation, thereby making close contact with the crucible 102. The principle of this disclosure is applicable to both heating techniques. Thus, the coil 116 is more broadly referred to as the heating means below and encompasses both induction heating and resistance heating (or a combination thereof). Furthermore, it should be noted that in this disclosure, the coil winding is illustrated as having a round, specifically circular or elliptical cross-section. However, the coil winding may have any other suitable cross-section, such as square or rectangular.

[0051] In the example shown in Figure 1, all the windings of the coil 116 are offset along the central axis 120 to have an increased slope. Thus, two opposing regions of each winding are offset axially by, for example, a distance d_1. As a result, a rotationally asymmetric temperature field is generated by the heating means during operation.

[0052] However, according to the principles of this disclosure, the thermal insulation unit 117 has a shape and structure that introduces an asymmetry that cancels out the asymmetric temperature field caused by the asymmetry of the heating means 116.

[0053] Figures 2–6 show various examples of how the thermal insulation unit 117 may be structured to provide insulating asymmetry that compensates for the effects of the asymmetry of the heating unit 116, which ultimately leads to a symmetrical temperature field in the crystal growth region 106 during single crystal Boolean growth.

[0054] For example, the thermal insulation unit 117 may have a body 300 formed from a sheet of carbon felt, which is wrapped around the crucible 102 (see Figure 1). A seam 304 is provided at the joint 302 of the two ends of the sheet to stabilize the body 300. The joint 302 with the seam 304 constitutes a discontinuity extending longitudinally along the central axis 120 (see Figure 1). This discontinuity must be located radially to create a discontinuity in the thermal insulation unit 117 to compensate for the asymmetry of the heating means 116. Of course, two or more joints 302, each with a seam 304, may be provided to achieve a very homogeneous temperature field acting on the growing single crystal.

[0055] The seams 304 are formed from threads made from carbon fiber. Other suitable materials that are non-conductive and have high thermal resistance may be used.

[0056] Instead of (or in addition to) the seam 102, the joint 302 may be stabilized by one or more fasteners 306. An example of this is shown in Figure 3. In this case as well, the joint 302 with fasteners 306 constitutes a discontinuity that extends longitudinally along the central axis 120 (see Figure 1). This discontinuity must be located radially, causing a discontinuity in the thermal insulation unit 117 to compensate for the asymmetry of the heating means 116. Of course, two or more joints 302, each having one or more fasteners 306, may be provided to achieve a very homogeneous temperature field acting on the growing single crystal.

[0057] The fastener 306 is manufactured, for example, from an impregnated and cured thread made from carbon fiber. Other suitable materials that are non-conductive and highly thermally resistant may be used.

[0058] Another example of providing a discontinuity in the thermal insulation unit 117 is shown in Figure 4. According to this advantageous example, one or more micro-holes 308 are provided in the body 300 of the thermal insulation unit 117. The micro-holes 308 may be formed to extend radially through the entire wall thickness of the body 300, thereby forming a gap. Alternatively, one or more micro-holes 308 may extend radially through only a portion of the wall thickness of the body 300, thereby forming a groove in the material of the body 300. The micro-holes 308 constitute a discontinuity that extends longitudinally along the central axis 120. This discontinuity must be located in a radial position that creates a discontinuity in the thermal insulation unit 117 to compensate for the asymmetry of the heating means 116.

[0059] It should be noted that these various examples of introducing discontinuities within the main body 300 of the thermal insulation unit 117 may, of course, be combined with each other as needed to achieve a highly homogeneous temperature field acting on the growing single crystal.

[0060] A further example of the thermal insulation unit 117 is shown in Figure 5 as a top view.

[0061] In this example, the body 300 of the thermal insulation unit 117 is formed from a sheet of thermal insulation material, such as needle-processed carbon felt, which is wound multiple times around a central axis 120. To give a smooth inner surface 310 and a smooth outer surface 312, the end regions of the sheet have bevels 314, 316 that extend along the central axis 120. If the body 300 is formed from only one layer of thermal insulation material (not shown in the figure), the bevels 314 and 316 are in direct contact to close the thermal insulation unit 117 around the central axis 120. In the illustrated example, the body has a three-layer structure. The sheet forming the body 300 is wound helically around the central axis 120 to form a circular, straight cylinder. In the joint region 318, the inner layer has a twisted region that provides inclined support surfaces 320, 322 for the bevels 314, 316 of the end regions.

[0062] The joining region 318 of the main body 300 provides a discontinuity that extends longitudinally along the central axis 120. This discontinuity must be located in a radial position that creates a discontinuity in the thermal insulation unit 117 to compensate for the asymmetry of the heating means 116.

[0063] Figure 6 schematically illustrates a further example of how the thermal insulation unit 117 can be given a discontinuity to counteract the asymmetry of the temperature field generated by the heating means during operation. As shown in Figure 6, the body 300 of the thermal insulation unit 117 has a substantially cylindrical shape with wall thicknesses that vary radially around the circumference of the body 300. For example, in the region covering more than 10° to less than 180° of the circumference, preferably more than 10° to less than 90° of the circumference, the wall 324 of the body 300 has a reduced thickness d2 compared to the rest of the circumference where the wall 324 has a thickness d1. Of course, the discontinuity may be created by providing a region of the body 300 with a thickness d2 greater than the thickness d1 in the rest of the circumference. The discontinuity may be abrupt or gradually developing.

[0064] Thus, a discontinuity is generated that extends longitudinally along the central axis 120. This discontinuity must be located in a radial position that causes a discontinuity in the thermal insulation unit 117 to compensate for the asymmetry of the heating means 116.

[0065] Returning to the various possibilities of providing a heating means 116 that creates an asymmetric temperature field acting on a growing single crystal without the use of further countermeasures, Figure 7 shows a sublimation system 100 according to a further example of the present disclosure. Note that the principle is essentially the same as that described with reference to Figure 1.

[0066] In detail, the sublimation system 100 comprises a growth crucible 102, which includes raw material compartments, in particular a SiC supply area 104 and a crystal growth area 106. The SiC raw material 108 is injected into the SiC supply area 104 of the growth crucible 102 as a pre-processed starting material before the start of the growth process, and is placed, for example, in the SiC supply area 104. A seed crystal 110 is provided in the crystal growth area 106, on the inner wall of the growth crucible 102 facing the SiC supply area 104, for example, on the lid 112 of the crucible. The bulk SiC single crystal to be grown grows on the seed crystal 110 by deposition from the SiC growth gas phase formed in the crystal growth area 106.

[0067] The growing crucible 102, including the crucible lid 112, may be manufactured from a conductive and thermally conductive graphite crucible material. A thermal insulation unit 117 is placed around it, which may be manufactured according to the principles described above, for example with reference to any of Figures 2 to 6.

[0068] In induction heating, the thermally insulated growth crucible 102 is placed inside a tubular container (not shown in Figure 1), which may be a quartz glass tube forming an autoclave or reactor. An induction heating device in the form of a heating coil 116 is positioned around the container to heat the growth crucible 102. The heating coil 116 generates the required temperature field by inductively coupling an electric current within the conductive crucible wall (susceptor) of the growth crucible 102. This current flows substantially as a circulating current circumferentially within the circular and hollow cylindrical crucible wall, heating the growth crucible 102 in the process. The susceptor can be made from graphite, TaC, WC, Ta, W, or other heat-resistant metals, and may be an integral part of the crucible 102 or a separate part close to the crucible wall. The primary purpose of the susceptor is to provide a heat source inside the crucible 102. When the susceptor is heated by induction, its surface reaches a high temperature, and that temperature is then transferred to the inside of the crucible 102 through conduction and / or radiation.

[0069] As described above, in the case of induction heating, the coil 116 is mounted on the outside of the glass tube and is usually surrounded by a Faraday cage (not visible in Figure 1) to block electromagnetic radiation. In the case of resistance heating, the coil 116 is also mounted inside the reactor and in thermal insulation, thereby making close contact with the crucible 102. The principle of this disclosure is applicable to both heating techniques.

[0070] As shown in Figure 7, the coil 116 has at least one deformation region 115 in which the cross-section of the coil 116 deviates from the circular cross-section of the remaining windings. In Figure 7, this deviation is depicted as a compression leading to an elliptical cross-section within the deformation region 115. Of course, other cross-sectional irregularities may exist in the coil 116. In the deformation region 115, the distance between the deformed winding and the adjacent winding is increased to a distance d_2 compared to the normal distance d_1 between the remaining undeformed windings. The location and extent of these irregularities may be discovered by inspecting the heating system, for example, if the crystal growth cycle performed has produced an unsatisfactory single crystal boolean. The asymmetric thermal insulation according to this disclosure can then be used to counteract the irregularities in the heating system.

[0071] During operation, structural asymmetry resulting from this deformation region 115, which can cover, for example, 10° to 90°, preferably 10° to 45°, of the circumference, introduces irregularities in the temperature field. These irregularities extend both radially (around the circumference of the crucible) and axially (along the central axis 120).

[0072] As a result, a rotationally asymmetric temperature field is generated by the heating means during operation.

[0073] However, according to the principle of this disclosure, the thermal insulation unit 117 has a shape and structure that introduces asymmetry that cancels out the asymmetric temperature field caused by the asymmetry of the heating means 116. Therefore, the temperature field to which the growing single crystal is exposed becomes homogeneous and symmetrical, making it possible to grow a high-quality crystal with as few edge defects as possible.

[0074] Furthermore, structural asymmetry may also be introduced into the sublimation system 100 if the electrical contacts 124 of the heating coil 116 must be located within the area surrounding the crucible 102. An example of this is shown in Figure 4. At least one of the electrical contacts 124 supplying current is located in the axial region rather than at the circumferential end of the heating coil 116, thereby constituting structural asymmetry near the crucible 102, particularly near the crystal growth region 106. Thus, during operation, the heating coil 116 generates a non-uniform temperature field unless it is counteracted by the asymmetry of the thermal insulation unit 117. As described above, according to the principles of this disclosure, the thermal insulation unit 117 has a shape and structure that introduces asymmetry that counteracts the asymmetric temperature field caused by the asymmetry of the heating means 116. Thus, the temperature field to which the growing single crystal is exposed becomes homogeneous and symmetrical, making it possible to grow a high-quality crystal with as few edge defects as possible.

[0075] Figure 9 shows a top view of the sublimation system 100 according to a further advantageous example. As shown in this figure, the asymmetry of the temperature field may be created by an asymmetric shielding 126 and a metal holder 132 of the shielding 126. The holder 132 may extend, for example, into the gap between the coil 116 and the shielding 126. The reactor 114 comprises the crucible and thermal insulation unit described above.

[0076] Therefore, during operation, the heating coil 116 generates a non-uniform temperature field, which is compensated for by the discontinuity (or multiple discontinuities) provided in the thermal isolation unit by this disclosure. Thus, the growing single crystal experiences a uniform temperature field, which leads to a high-quality crystal boule with very few edge defects.

[0077] Moving on to Figure 7, the principle of this disclosure may be further applied to a sublimation system 200, which is capable of operating to grow two single-crystal boules simultaneously. For this purpose, the crucible 202 comprises a first seed crystal 210A and a second seed crystal 210B. Figure 7 shows an example similar to the configuration shown in Figure 4. However, it is clear that other possibilities for how an asymmetric temperature field may occur may exist in the sublimation system 200 for growing two or more single-crystal boules simultaneously, as described, for example, in European Patent Application Publication No. 2664695(B1).

[0078] More specifically, Figure 7 shows a schematic cross-sectional view of a physical vapor transport (PVT) growth system 200 for simultaneously growing two SiC bulk crystals. The system 200 comprises a crucible 202, which includes a central raw material compartment 234 containing SiC powder 208, which is the raw material for SiC. The raw material 208 may be densified or provided as a partially or completely solid material to increase its density.

[0079] Two seed crystals 210A and 210B are placed in growth regions 206A and 206B. Each of the growth regions 206A and 206B is separated from the powdered SiC raw material 208 by gas-permeable porous barriers 236A and 236B. Thus, it is ensured that only gaseous Si and C-containing components enter the growth regions 206A and 206B.

[0080] The heating coil 216 provides the required temperature field. Asymmetry in the temperature field is caused, for example, by electrical contacts 224 near the crystal growth regions 206A and 206B.

[0081] To compensate for the asymmetry of the temperature field generated by the heating means 116, the thermal isolation unit 117 provides a discontinuity (or two or more discontinuities) to cancel it out, as described in the example above. Thus, the growing single crystal experiences a uniform temperature field, which leads to a high-quality crystal Boule with very few edge defects.

[0082] In summary, the present invention is based on the finding that by using a special isolation design, it is possible to grow high-quality crystals with as few edge defects as possible, despite the use of a growth system that generates a heterogeneous temperature field.

[0083] Since the ideally homogeneous isolation provided according to current technology in combination with growth systems involving heterogeneous temperature fields is clearly insufficient to obtain the desired crystal quality, the method presented in this disclosure balances the overall heterogeneity by using locally heterogeneous isolation to grow SiC single crystals in a heterogeneous growth system, thereby generating a homogeneous temperature field in the region of the growing crystal. For this purpose, several conditions must be met.

[0084] The technical problem of growing crystals without edge defects is, on the one hand, solved by using a growth system that generates at least one heterogeneous and radially asymmetrical heat input to the growth crucible.

[0085] Heterogeneous and asymmetrical thermal bonding can be caused, for example, by the following characteristics of the growth system: - Unequal spacing of coil windings in the heating system due to winding offset. - Unequal spacing of coil windings due to uneven winding configuration - Inlet and outlet for coil / resistance heater within the susceptor and / or growth crucible area. - The winding ends of the coil (within the area of ​​the susceptor and / or growth crucible) - Brackets or supports (metal) that are directly above the coil or between the coil windings, which distort the induction. - Use of asymmetrical shielding of electromagnetic fields

[0086] The technical problem of growing crystals without edge defects is solved, on the other hand, by using heterogeneous isolation in combination with the growth equipment described above to create a homogeneous field within the crystal growth space as a whole.

[0087] This isolation may have the following characteristics, which result in heterogeneity or discontinuity: - Overlapping needle-processed carbon fiber, rolled, stitched, fastened, and / or folded webs - Rolled, stitched, fastened, and / or folded webs of needle-processed carbon fiber with no overlap and straight butt joints. - Rolled, stitched, fastened, and / or folded webs of needle-processed carbon fiber with beveled joints. - A multi-part design having at least two sheets of needle-processed carbon fiber having a butt joint or overlapping ends and / or seams in multiple locations. - Single or multi-part design with stitching on the opposite side of the joint or overlap - Stitching in several positions, stitching on four sides at a 90° angle - Combination of needle-processed carbon fibers with compressed short fibers - Single or multi-part design consisting of a cylinder with micro-pores made of compressed short fibers - A cylinder made of compressed short fibers having discontinuities and / or joints by seams and / or glued joints. - Use of stepped or locally thinned cylinders made of needle-processed carbon fibers and / or compressed short fibers. - Perforation of a cylinder of needle-processed carbon fibers and / or compressed short fibers, having discontinuities along and / or across the radial axis of symmetry of the growth cylinder. - Insertion of a defined gap between the insulating cylinder, base, and / or lid for control of the local temperature field.

[0088] Inhomogeneities or discontinuities within an insulation lead to localized changes in insulation properties. Therefore, where there are no overlapping junctions, the insulating effect can be reduced by interrupting the ring current (a ring current can also be slightly generated in the insulating material by the coupled induced magnetic field). In this way, defects such as the aforementioned carbon impurities and / or carbon particles can be avoided, as localized hot spots generated by the system due to the system design can be compensated for.

[0089] By combining the asymmetric isolation and asymmetric growth systems described herein, a homogeneous field is generated within the growth chamber, thereby enabling the growth of homogeneous, edge-defect-free SiC single crystals.

[0090] The growth rate, measured at two points on the diameter of the substrate fabricated from the crystal, may deviate by at least 0.1 μm / h, but must not deviate by more than 10 μm / h, preferably 7 μm / h. This condition leads to uniform growth in the edge region across the entire circumference of the crystal and suppression of edge defects.

[0091] The introduction of this targeted asymmetric insulation into the asymmetric growth system, in combination, results in a homogeneous temperature field within the growth chamber. As a result, homogeneous, virtually edge-defect-free SiC single crystals can be grown.

[0092] The present disclosure provides a method for producing at least one SiC volume single crystal by sublimation growth, in which a SiC seed crystal fixed to a holding device is placed prior to the initiation of growth in the crystal growth region of a growth crucible partially formed from graphite, powdered or (partially) compressed SiC raw material is introduced into the SiC supply region of the growth crucible, and the crucible is sealed with an insulator. Thereafter, during growth at a growth temperature of up to 2400°C generated by thermal coupling of induction coil or resistance heating, and a growth pressure of 0.1 mbar to 100 mbar, a SiC growth gas phase is generated therein by the sublimation of the SiC raw material and the transport of the sublimated gaseous component into the crystal growth region, and within this SiC growth gas phase, a SiC volume single crystal grows on the SiC seed crystal by deposition from the SiC growth gas phase.

[0093] The equipment used for sublimation incubation has heterogeneity and asymmetry inherent in its design. Simultaneously, heterogeneous and / or discontinuous isolation is used.

[0094] By combining the heterogeneity of the growth system design with the heterogeneity or discontinuity of the insulation, a homogeneous temperature field can be generated within the reactor, particularly within the crystal growth region. This is achieved by orienting and aligning the insulation heterogeneity with respect to the plant asymmetry, which is determined by prior experimental testing. Similarly, in the case of multiple plant asymmetries, heterogeneous isolation can be balanced by multiple heterogeneities.

[0095] The resulting homogeneous temperature field within the crystal growth region, which acts on the growing crystal, enables the production of crystals with virtually no edge defects.

[0096] Furthermore, the growth rates measured at two points on the diameter of the fabricated substrate may differ by at least 0.1 μm / h, but may deviate by a maximum of 10 μm / h, preferably 7 μm / h. The difference between the maximum and minimum lengths between the crystal surface and the crystal back surface at the outer diameter of the crystal may differ by 10% or less from the average crystal length measured from the outer diameter of the crystal. Preferably, the difference between the maximum and minimum lengths between the crystal surface and the crystal back surface at the outer diameter of the crystal may differ by 5% from the average crystal length measured from the outer diameter of the crystal.

[0097] The average length difference between the crystal surface and the crystal back surface, measured for the diameter of the finished wafer, must be approximately at least 1 mm smaller than the maximum length difference between the crystal surface and the crystal back surface, but must not be less than 6 mm smaller.

[0098] The difference in length may be measured at the edge of the crystal, but it may also be measured at the diameter corresponding to the diameter of the finished wafer.

[0099] The principle of this disclosure can be used to grow SiC single crystal boules for producing substrates in crystal varieties of 4H, 6H, 15R, 3C, preferably 4H. The grown single crystal boules may have a crystal diameter of approximately 150 mm or more, preferably approximately 200 mm. [Explanation of Symbols]

[0100] 100, 200 sublimation system, PVT system 102, 202 Crucible 104 SiC supply area, raw material section 106, 206A, 206B Crystal growth region 108, 208 Ingredients 110, 210A, 210B seed crystals 112 Crucible Lid 114 Vessels, reactors 115 Deformation Region 116, 216 Induction or resistance heating coil, heating means 117 Thermal Insulation Unit 119 Transparent window 120, 220 center axis 122 Displacement Region 124, 224 electrical contacts 126 Shielding 132 Holder 234 Raw materials section 236A, 236B barrier 300 main unit 302 Joint 304 stitches 306 Fasteners 308 Small hole 310 Inner surface 312 Outer surface 314 Slope 316 Slope 318 Joint area 320 Inclined support surface 322 Inclined support surface 324 Main body wall 800 PVT system 802 Crucible 804 SiC supply area 806 Crystal growth region 808 Ingredients 810 seed crystals 812 Crucible Lid 814 Containers, reactors 816 Induction heating coil

Claims

1. A sublimation system for growing at least one single crystal of a semiconductor material by sublimation growth, wherein the sublimation system (100) is A crucible (102) having a longitudinal axis (120) and comprising fixing means for at least one seed crystal (110) and at least one raw material compartment (104) for containing raw material (108), A heating system formed to generate an irregular temperature field around the circumference of the crucible (102) and / or along the longitudinal axis of the crucible (102), A thermal insulation unit (117) that at least partially surrounds the crucible (102), wherein the thermal insulation unit (117) has a radially and / or axially asymmetrical configuration for compensating for the irregular temperature field, A sublimation system equipped with this feature.

2. The heating system comprises an induction coil in the form of an induction heating coil adapted for induction heating, and / or a resistance heating coil adapted for resistance heating, wherein the induction coil and / or the resistance heating coil at least partially surround the crucible (102), and The sublimation system according to claim 1, wherein the induction coil operates to generate an electromagnetic field.

3. The sublimation system according to claim 1 or 2, wherein the thermal insulation unit (117) comprises needle-processed carbon felt and / or high-density carbon short fibers.

4. The sublimation system according to any one of claims 1 to 3, wherein the thermal insulation unit (117) comprises a flexible sheet of carbon material, the sheet being wound around the crucible (102) and comprising a seam (304), at least one fastener (306), and / or overlapping area.

5. The sublimation system according to any one of claims 1 to 4, wherein the heating system comprises a metal support member.

6. The sublimation system according to any one of claims 2 to 5, wherein the induction coil and / or the resistance heating coil has a cross-section that is deformed to at least one of its windings, and / or the induction coil and / or the resistance heating coil has at least one winding that is arranged to be at different distances from adjacent windings.

7. The sublimation system according to one of claims 2 to 6, wherein the induction coil and / or the resistance heating coil comprises at least one electrical contact (124) positioned in an axial location adjacent to the crucible (102).

8. The sublimation system according to any one of claims 1 to 7, wherein the thermal insulation unit (117) has a cylindrical shape in which the wall thickness changes around the circumference.

9. The sublimation system according to any one of claims 1 to 8, wherein the thermal insulation unit (117) comprises one or more small holes (308) that form at least one gap or groove.

10. The sublimation system according to one of claims 1 to 9, wherein the thermal insulation unit (117) is formed by a plurality of separate parts assembled to have radial and / or axially extending connections.

11. The sublimation system according to one of claims 1 to 10, wherein the thermal insulation unit (117) is formed of a sheet of insulating material, and the sheet is arranged around the crucible to form abutment joint, an inclined abutment joint, and / or overlapping joint.

12. A method for growing at least one single crystal of a semiconductor material by sublimation growth, A crucible (102) having a longitudinal axis is prepared, at least one seed crystal (110) is fixed to the fixing means of the crucible, and at least one raw material compartment (104) is filled with raw material (108), This includes using a heating system to generate an irregular temperature field around the circumference of the crucible (102) and / or along the longitudinal axis of the crucible (102), A method comprising a thermal insulation unit (117) that at least partially surrounds the crucible (102), wherein the thermal insulation unit (117) has a radially and / or axially asymmetrical configuration for compensating for the irregular temperature field.

13. The method according to claim 12, wherein the temperature field acting on the growing single crystal causes the growth rate measured around a defined circumference of the single crystal to differ by at least 0.1 μm / h to 10 μm / h or 0.7 μm / h at any two locations along the circumference.

14. The method according to claim 12 or 13, wherein the temperature field acting on the growing single crystal gives the finally grown single crystal a distribution of length values ​​between the back surface of the single crystal and the top surface of the single crystal, measured along a defined circumference of the single crystal, wherein the length values ​​differ from the average value by 10% or less, or by 5% or less.

15. The method according to claim 13 or 14, wherein the defined circumference is the outer circumference of the finally grown single crystal, or the defined circumference is the radial distance from the center of the finally grown single crystal that corresponds to the diameter of the substrate manufactured from the finally grown single crystal.

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